With the exception of Antwerp no Belgian municipalities reach a population of 500.000. While the Brussels metro area is much larger, the city proper doesn't even exceed 200.000.
As far as I am aware none of the cities is southeastern England (except for London) reach the threshold of 500.000 population. Several English cities are very similar distances away from Amsterdam, but Sheffield and Leeds are the closest. Birmingham misses out by just a handful of kilometers.